1. Field of the Invention (Technical Field)
The present invention relates to a pelletizing device comprising a die with a first surface, called operative surface, and a second surface that is essentially parallel to the first surface, the die between the first and the second surface comprising multiple through going openings for the forming of pellets, at least two rollers rotatable around a shaft, wherein the rollers and the die are moveable with respect to each other, each of the rollers comprising an operative pressing surface for pressing material to be pelletized through the radial openings of the die. The invention also relates to rollers for the device.
2. Description of Related Art
In many industries products are offered in pellet form. These pellets have the form of large grains or small rods and are produced from originally fine grained material. This material in pellet form can easily be handled, be stored, be packaged and transported. Examples of pellets can be found in the cattle food industry, the recycling industry, but also plastics industry and biomass industry.
For example in wood industry sawdust and/or wood chips are being pressed to pellets, that then easily can be packaged and transported, but also properly metered can be fed to for instance incinerators and boilers.
The forming of pellets takes place in pelletizing devices. Pelletizing devices exist in different designs. Generally all designs comprise a die with a first surface, called operative surface, and a second surface that is essentially parallel to the first surface. The die comprises multiple through going openings for the forming of pellets between the first and the second surface. The pelletizing devices also comprise at least one roller rotatable around a shaft, wherein the rollers and the die are moveable with respect to each other, each of the rollers comprising an operative pressing surface for pressing material to be pelletized through the radial openings of the die. Pelletizing devices exist with a flat operative surface of the die and other devices have a cylindrical operative surface of the die. The roller(s) and die are moveable with respect to each other such that the roller(s) are rolling with their operative pressing surfaces over the operative die surface to press the material to be pelletized, that has been placed on the operative die surface, through the through going openings in the die and thus creating the pellets. The rollers may be driven to roll over the die, but also the rollers may be not-driven but the die is moved under the rollers or a combined driven movement is possible. The width of the operative pressing surface each roller is equal to or slightly larger than the width of the operative surface of the die. The roller is situated at a predefined minimal distance of the inside of the die and between the roller and the die the material to be pelletized is being compressed into the radial openings in the die. If the die is driven, the roller need not to be driven separately but gets into rotation by the rotation of the die and the material to be pelletized that is situated between the die and the roller. It is also possible to have the rollers rotating and the die stationary. During the pressing of pellets large forces are being generated. To generate these forces, the die or rollers are being driven with considerable power.
Within the principles described above there are still quite some variants possible in the design of the pelletizing devices. For instance a design variant can be found in the number of rollers used. One possibility is to have just one roller. However most commonly today machines are found with two or more rollers. This is mainly due to the large forces that are generated during the pressing of pellets as mentioned before. These forces are acting on the roller and in case of one roller the construction to keep this roller stable under these large forces can become complicated, heavy and above all costly. When two rollers are being used the construction to keep the rollers in a stable position becomes far easier. Also the same goes for three or more rollers possibly to a somewhat lesser extent.